Poly solution photolysis

Solution Photolysis of Poly(p-acetoxystyrene) A 2.576 g sample of III was dissolved in 350 ml of acetonitrile and placed in a 500 ml Hanovia reactor equipped with a water-cooled quartz finger and 500 watt mercury arc lamp, condenser, nitrogen inlet and bubbler. The solution was irradiated for a total of... 

Solution Photolysis of Poly(p-Formyloxystyrene) A 2.0 g sample of poly(/7-formyloxystyrene) was dissolved in 300 mis of spectral grade acetonitrile, and the solution irradiated in the Hanovia apparatus. Small aliquots of the irradiating polymer solution were withdrawn and analyzed at regular intervals as described above. 

Pyridinium ylide is considered to be the adduct car-bene to the lone pair of nitrogen in pyridine. The validity of this assumption was confirmed by Tozume et al. [12J. They obtained pyridinium bis-(methoxycarbonyl) meth-ylide by the photolysis of dimethyl diazomalonate in pyridine. Matsuyama et al. [13] reported that the pyridinium ylide was produced quantitatively by the transylidalion of sulfonium ylide with pyridine in the presence of some sulfides. However, in their method it was not easy to separate the end products. Kondo and his coworkers [14] noticed that this disadvantage was overcome by the use of carbon disulfide as a catalyst. Therefore, they used this reaction to prepare poly[4-vinylpyridinium bis-(methoxycarbonyl) methylide (Scheme 12) by stirring a solution of poly(4-vinylpyridine), methylphenylsulfo-nium bis-(methoxycarbonyl)methylide, and carbon disulfide in chloroform for 2 days at room temperature. 

A considerable amount of attention has also been paid to the photo-Fries rearrangement of polymer pendant groups. For example, the rearrangement of poly (phenyl acrylate) (10,11) in solution or in the solid-state, is usually incomplete and results in the formation of both the ortho and the para-hydroxyphenone rearranged products in amounts which vary with the conditions of the photolysis. A concurrent side-reaction, which we term the Fries degradation, also results in the liberation of small amounts of phenol (Scheme 2). Similar results have been obtained with poly (phenyl methacrylate) and other substituted aryl acrylates (4,9,12). 

Once again photolysis experiments carried out with thin films or solutions of poly (p-formyloxystyrene) (IV) in dioxane or acetonitrile give essentially the same results. IR monitoring of the exposure (Figure 3) shows a... 

Solid-State Photolysis of Poly(p-Formyloxystyrene) A 10% solution of poly(p-formyloxystyrene) (IV) (Mn 18,000) in diglyme was prepared under... 

After photolysis at room temperature of the degassed aqueous solutions of colloidal Ti02 (anatase, 2R = 10-15 run) in the presence of poly(vinyl alcohol) (PVA), EPR spectra recorded at 77 K showed existence of several types of paramagnetic centers in the system... 

The photolysis of a large number of polychlorobenzenes, polybromobenzenes and poly-chloropolybromobenzenes (QH XJ in benzene solution has been studied371. In addition to dehalogenation, phenylation was observed, leading to (poly)halobiphenyls (QH X j—C6H5) and, by consecutive phenylation, to haloterphenyls. 

The Ni and Pt complexes can also be incorporated into polymer films of quaternized poly(vinylpyridine) (PVP) and deposited onto the transparent electrode (84). Photocurrents are enhanced to microamps (pA), an increase that may be attributed to either the effect of immobilization of the complexes near the electrode surface or an increase of the excited-state lifetimes in the polymer matrix. However, the effective concentrations of the complexes in this study were much greater than for the acetonitrile solutions in their earlier work. The polymer films are not stable to continuous photolysis, and voltammograms of the films are quite sensitive to anions used in the supporting electrolyte. The system can be stabilized by using a polymer blend of PVP and a copolymer containing quaternary ammonium ion and including [Fe(CN)6]4- in the electrolyte solution (85). Upon irradiation of the visible MLCT bands of [M(mnt)2]2 (M = Ni, Pt), photocurrents are produced. The mechanism (Scheme 4) is believed to involve photooxidation of the metal bis(dithiolene) triplet state by the Sn02 electrode, followed by [Fe(CN)6]4 reduction of the monoanion, with completion of the ET cycle as ferricyanide, Fe(CN)6 3, diffuses to the other electrode and is reduced. 

However, several inherent drawbacks limit the utility of aryldiazonium salts as photoinitiators in a number of practical applications for epoxy curing. Nitrogen evolution during photolysis of the initiator causes bubbles and pinholes in coatings. Other problems arise from the poor thermal stability of aryldiazonium compounds and from their inherent sensitivity to moisture. The addition of stabilizing additives such as nitriles amides sulfoxides and poly(vinylpyrrolidone) has proven effective in extending the solution stability of aryldiazonium salt/epoxy mixtures. 

The theory of rotation effects on prolate luminescent molecules in solution and its experimental verification have been developed and compared. Generalized diffusion equations for the rotational motion of an asymmetric rigid motor have been used to given an expression for steady-state fluorescence depolarization. " The radiationless transition from the first excited singlet state of Eosin has been measured by optoacoustic relaxation, and the absolute fluorescence quantum yields of organic dyes in poly(vinyl alcohol) have also been measured by the photoacoustic method. The accuracy of the method has been discussed in the latter paper. Actinometry in flash photolysis experiments has been assisted by new measurements on the extinction coefficient of triplet benzophenone. Matrix-isolation fluorescence spectrometry has been used to detect polycyclic aromatic hydrocarbons from gas chromatography. ... 

Phosphorescence studies in isobutylene-methyl methacrylate-1-naphthyl-methyl methacrylate co-polymer provided evidence to show that in very dilute solution the chain collapses into more compact structures, and intramolecular excimer formation in poly-(2-vinylnaphthalene) has been shown to exhibit non-Stokes-Einstein behaviour. Laser photolysis of polymers containing phenanthryl groups, such as poly-(9-vinylphenanthrene), indicates the presence of plural dimer sites having different geometries owing to the stacking effect of phenanthrene chromophores. In poly-(2-naphthyl methacrylate). 

According to a similar mechanism, the photolysis of poly[bis(4-benzo-ylphenoxy)phosphazene] [poly(BPP)] in air equilibrated CH2CI2 solution induces chain scission and extensive degradation of the macromolecules [14],... 

Free and polymer-bound 2-benzyloxy-thioxanthone exhibit similar flash photolysis behaviour and the same photoreduction quantum yield in the presence of 2-(A, AT-diethylamino) ethanol. This clearly shows that the polymeric nature does not appear to affect photophysical properties of the thioxanthone moiety. The photoinitiated polymerization of MMA in benzene solution, using BOTX and poly(StX-co-St) in combination with 2-(MA -dieffiylamino) ethanol, indicates that the polymer-bound chromophore seems to operate in the same way and with similar efficiency as the free photoinitiator, at least in conditions of dilute chromophore concentration. 

Indeed, photophysical studies by laser flash photolysis combined with the determination of MMA polymerization rate (Rp) in toluene solution, have allowed evaluation of the triplet state lifetime of the above systems, as well as their relative quantum yields of initiation ( j) and a-cleavage ( ). As reported in Table 22, 3, values for poly(MBA) and poly(MBVE) are appreciably lower than those for MBI and MBEE, respectively. On this basis, the polymeric photoinitiators would be expected to display lower activity than the models in the polymerization of acrylic monomers. On the contrary, poly(MBA) and poly(MBVE), together with the related copolymers, show higher values of Rp and hence i, in the UV initiated polymerization of MMA in toluene solution. These findings, therefore, confirm the previously obtained results in film matrix, where a HDDA/BA equimolar mixture was used as curing formulation (Table 21). 

The photolysis of poly-a-methylstyrene, both in solution [46] and as solid films [10], has been studied by Fox and coworkers. For solid films, a rapid drop in the molecular weight has been observed. The quantum yield of this process is 1 x 10-3 at 27°C and 2 x 10-2 at 115°C. Simultaneously, monomer is evolved with quantum yields of 7 x 10"3 and 5 x 10 1 at 27 and 115°C, respectively. Such behaviour has been ascribed to random breaking of the main chain followed by depolymerization [10] namely,... 

---